"One more thing," for short

• Start of a chat room afterthought
• Incidentally, in a txt msg
• Letters before an emailed aside
• Digression shorthand
• "Oh, I almost forgot," in a text
• Incidentally, in texting shorthand
• "As an aside ...," in a text
• Texter's afterthought lead-in
• "Incidentally," in a text

Douglas Harper's Etymology Dictionary Word definitions in Douglas Harper's Etymology Dictionary
Internet abbreviation of by the way , in use by 1989.